A principal application for optical imaging systems is the detection, recognition, and identification (DRI) of objects.
Hence, an often-encountered requirement of these optical systems is that they be able to provide an image of a scene having a wide field of view (WFOV) and low magnification and another image of the scene having a narrow field of view (NFOV) and relatively higher magnification, thus forming a dual field of view optics, for example with a magnification ratio of at least three times between fields of view.
Optical imaging systems that respect this requirement often use complex multiple component systems. Generally, one lens or system of lenses is used to provide the WFOV image of the scene while another lens or systems of lenses is used to provide the NFOV image. There exist optical systems where one basic set of lenses common to both the WFOV and NFOV image acquisition is used in conjunction with additional field-of-view-specific lenses to acquire the specific field of view image. In such optical systems, the additional lenses are selectively inserted into the optical path to select the desired field of view (FOV). The selection mechanism of such systems can be voluminous adding to the overall size of the optical imaging system. As the number of optical components of an optical system increases, the adjustment of the components becomes more complicated and the overall weight and size of the system tends to increase.
In order to separately view the two images of different fields of view that are formed, optical imaging systems include a detector onto which the image is focussed.
In some prior art systems, each of the two images of different fields of view is assigned a separate location on the detector using additional optical components such as prisms or filters to redirect or shift one or both of the images onto the detector. However, with this approach to image detection, the quality and to resolution of each of the images is less than optimal since only a portion of the total pixels of the detector are actually used for each of the images.
In other prior art systems, elements of the lens system are moved along the optical path to a position where one image of the scene is focussed onto the entire surface of the fixed detector and are then moved along the optical path to another position where the other image is now focussed onto the entire surface of the fixed detector. It is also known to use two different detectors to image a scene with two different fields of view. Of course, this latter method can make for a more expensive and more voluminous system.
There is therefore a need for an optical imaging system, which reduces the number of optical components and provides two images of a scene, each having a different field of view, by using the entire active surface of a detector.